Filter out unique value from object inside array using loadsh

Question

I am trying to get the unique category from the following array using loadsh,

[{
  "listingId": "p106a904a-b8c6-4d2d-a364-0d21e3505010",
  "section": "section1",
  "category": "VIP PASS ",
  "type": "paper",
  "availableTickets": 1
}, {
  "listingId": "p106904a-b8c6-4d2d-a364-0d21e3505010",
  "section": "section1",
  "category": "VIP PASS ",
  "type": "paper",
  "availableTickets": 2
}, {
  "listingId": "pc8f54389-4e58-482a-9535-6917c2948764",
  "section": "1",
  "category": "WIP",
  "type": "paper",
  "availableTickets": 1
}]

This is what i have tried

 this.categories = _.uniq(this.listings, function (test: ListDAO) { return test.category; });

but the above returns the same array again. how can i get the output result as,

VIP PASS and WIP

tymeJV · Accepted Answer · 2017-07-17 18:23:44Z

3

Without lodash and using .reduce:

let arr2 = arr.reduce((a, i) => a.indexOf(i.category) > -1 ? a : a.concat(i.category), []);

https://jsfiddle.net/42my6p08/

answered Jul 17, 2017 at 18:23

tymeJV

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7 Comments

user7426734 Over a year ago

how to change this to support typescript

Naftali Over a year ago

@faceturn that is valid js/typescript (as is mine)

user7426734 Over a year ago

is there a way to automatically remove empty string?

tymeJV Over a year ago

@faceturn - You can use .filter afterwards - .filter(c => !!c)

user7426734 Over a year ago

this.listings.reduce((a, i) => a.indexOf(i.category) > -1 ? a : a.concat(i.category), []).filter(c => !!c);

|

Naftali · Accepted Answer · 2017-07-17 18:32:21Z

2

You need to use uniqBy as uniq only accepts a regular array with no callback for each.

https://lodash.com/docs/4.17.4#uniqBy

You can try this:

this.categories = _.uniqBy(this.listings, ({ category }) => category);

If you want just the strings (as per comments) you can just do:

const getCategory = ({ category }) => category;

this.categories = _.uniqBy(this.listings, getCategory).map(getCategory);

(can also use the same callback function from your OP instead of mine.)

edited Jul 17, 2017 at 18:32

answered Jul 17, 2017 at 18:21

Naftali

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15 Comments

user7426734 Over a year ago

it does not work with typescript , there is an error on category

Naftali Over a year ago

You can still use your same old callback function (test: ListDAO) { return test.category; } @faceturn

user7426734 Over a year ago

this.ticketCategories = _.uniqBy(this.listings, function (test: ListDAO) { return test.category; });

user7426734 Over a year ago

the above return correct unique objects , not string values as mentioned

Naftali Over a year ago

again you can use your same callback... I was just making it smaller using es6 fanciness.

|

Hassan Imam · Accepted Answer · 2017-07-17 19:23:37Z

0

A solution using Map and reduce.

var arr = [{
  "listingId": "p106a904a-b8c6-4d2d-a364-0d21e3505010",
  "section": "section1",
  "category": "VIP PASS ",
  "type": "paper",
  "availableTickets": 1
}, {
  "listingId": "p106904a-b8c6-4d2d-a364-0d21e3505010",
  "section": "section1",
  "category": "VIP PASS ",
  "type": "paper",
  "availableTickets": 2
}, {
  "listingId": "pc8f54389-4e58-482a-9535-6917c2948764",
  "section": "1",
  "category": "WIP",
  "type": "paper",
  "availableTickets": 1
}];

var unique = arr.reduce((map, o) => (map.has(o.category) ? map : map.set(o.category)),new Map());
console.log(Array.from(unique.keys()));

answered Jul 17, 2017 at 19:23

Hassan Imam

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